Investigations of two-step energy transfer process induced near-infrared quantum cutting in YNbO4: Er3+/Yb3+ phosphors

Effective near-infrared (NIR) quantum cutting (QC) is extremely significant for light conversion materials used in silicon-based solar cells. Therefore, it is necessary to elucidate the mechanisms for the QC process in the light conversion materials. In view of that, a series of Er3+ single doped and Er3+/Yb3+ codoped YNbO4 phosphors were prepared to explore the mechanisms for QC and further calculate the QC efficiency. At first, the QC mechanisms for Er3+/Yb3+ codoped YNbO4 phosphors were investigated at length by analyzing the luminescent intensity of donor Er3+ and acceptor Yb3+ in visible and infrared spectra. Two-step energy transfer expressed as ET1: S-4(3/2)+F-2(7/2) -> I-4(11/2) +F-2(5/2) and ET2: I-4(11/2) + F-2(7/2) -> I-4(15/2) + F-2(5/2) was discovered to be responsible for the QC behavior. Furthermore, the calculations of QC efficiency were carried out in the framework of the two-step energy transfer efficiencies based on F & ouml;ster-Dexter theory, radiative transition rates based on Judd-Ofelt (J-O) theory, nonradiative relaxation rates between all 4f energy levels based on energy gap law and fluorescence lifetimes of relevant energy levels. The better QC efficiency was confirmed to be about 136 % in YNbO4:1 mol% Er3+/20 mol% Yb3+ sample, thus indicating that YNbO4: Er3+/Yb3+ phosphors are promising candidates in the light conversion materials.